Direct summertime flights to La Rochelle with low-cost carriers from various UK airports including Gatwick, Stansted, Southampton. The island is connected to the mainland by a toll bridge.
There is a coach service which connects the train station in La Rochelle (in winter) or the airport (in summer) to all of the villages on the island, and taxis are also available to take you across to La Flotte. Once there you can also cycle and walk back and forth across the bridge for free.
If you are driving down in the summer, consider avoiding Marans, a small village at the top of the Charante-Maritime, as traffic can get quite bad there.